Laminated safety glass



J n 11, 1968 F. 'r. BUCKLEY ETAL 3,338,033

LAMINATED SAFETY GLASS Filed Jan. 13, 1965 YVl/VYL BUT'YQAL PLASTIC/ZEDM7 pl/OSPHATE Pal. YCARBO/VA TE YV/NYL BUTYRAL PL 1457767250 M7PHOSPHATE GLASS INVENTOR. FRANCIS 7. BUCHEV ARRY R- MASON PA YMOND F.215% By W AhSTRACT 05* THE DESQLOSURE Laminates of polyaryl carbonateand polyvinyl acetal which have been plasticized with a phosphate. Theinitial laminate may be sandwiched between sheets of transparent panelsuch as glass.

This invention relates to a laminated article and more particularly tothe lamination of polycarbonate and glass.

It has been proposed heretofore to prepare a safety glass by laminatingglass with polycarbonate. More particularly, it has been found thatwhere glass and polycarbonate are laminated together with an interlayerof polyvinyl butyral, a strong lamination results which has high impactstrength. The conventional plasticizer for polyvinyl bu'tyral which isused to prepare safety glass is highly unsatisfactory for thepreparation of glasspolycarbonate laminates. Conventional plasticizersfor the polyvinyl butyral causes degradation of the polycarbonate sothat the laminated product becomes crazed in a very short time.

It is not practical to make safety glass by bonding polycarbonatedirectly to glass because polycarbonate and glass have differentco-efiicients of thermal expansion.. A safety glass made by bondingpolycarbonate directly to glass will crack and spall the glass oncooling from the temperature necessary to bond the two together due todifferent amounts of contraction.

It is therefore an object of this invention to provide a laminatedarticle based on a polyarylcarbonate and glass as well as precursorlaminates which are free of the foregoing disadvantages. Still a furtherobject of this invention is to provide a plasticized polyvinyl butyralwhich can be used to laminate glass to polycarbonate without thedifficulties experienced with conventional plasticized polyvinylbutyrals. Another object of this invention is to provide aglass-polycarbonate laminant which has high load bearing properties.Still a further object of this invention is to provide a laminatedarticle of polycarbonate and glass which has good light transmission andgood strength properties over a wide temperature range.

These and other objects of the invention will become apparent from thefollowing description and the accompanying drawing.

The foregoing objects and others are accomplished in accordance withthis invention, generally speaking, by providing a laminated articlecomprising a polyarylcarbonate and a polyvinyl acetal plasticized with aphosphate. Thus, these laminates comprise a polyarylcarbonate bonded toglass or other pellucid sheet-like material with a polyvinyl acetalwhich has been plasticized with a phosphate which preferably has theformula R PO wherein R is as defined below and comprise precursorlaminates adapted to prepare such a laminated article. Therefore, thisinvention contemplates as a preferred embodiment a laminated article ofpolyarylcarbonate, polyvinyl acetal and glass, said polyvinyl acetalbeing plasticized with from about 5% to about 60% by weight and mostpreferred 10-45% by weight of a phosphate.

States Patent 0 "ice The laminated article of the present invention ispreferably made up of five sheets; two of glass, two of polyvinyl acetalplasticized with phosphate and one of polyarylcarbonate. Thepolyarylcarbonate forms the center layer which is sandwiched between twosheets of polyvinyl acetal which is in turn sandwiched between twosheets of glass. Still further the invention contemplates a prelaminateof part of the sheets which form the final laminate. For example, it ispossible to sandwich a sheet of polyarylcarbona-te between two sheets ofpolyvinyl acetal which has been plasticized with a phosphate inaccordance with the invention by lightly or even firmly pressing themtogether. This three part prelaminate which is in and of itself new anduseful may then be used either immediately or at a much later time as aninterlayer for the glass or glass-like sheets to prepare the multiplelaminate. The preliminary sandwich in particular has the advantage ofbeing prepared at one location by specialists in the thermoplasticsfield for use by laminators subsequently at another location. Inaddition to the foregoing economic and practical desirability for makinga prelaminate, there is an unexpected technical advantage also. Theprelaminate is much easier to adhere to glass because thepolyarylcarbonate cannot take up moisture after being sandwiched betweenthe sheets of polyvinyl acetal. The process steps desirable for adheringpolyvinyl acetals to polyarylcarbonates are not always satisfactory foradhering polyvinyl acetals to glass. By making a prelaminate oneovercomes these difficulties.

The polyvinyl acetal plasticized with the phosphate is the crux of thepresent invention. It is well known to laminate glass with variousplastics including plasticized polyvinyl acetals. However, theconventionally plasticized polyvinyl acetals, for example, polyvinylbutyral containing triethylene glycol di-(Z-ethyl butyrate) isunsatisfactory for laminating glass to polycarbonate. The laminatedstructure based on the conventional plasticized polyvinyl butyraldevelops stress cracks in the polyarylcarbonate in a short time and soonthe amount of light transmission through the laminated article dropsbelow permissible levels. When the phosphate is employed preferably inan amount of from about 5 to 60% by weight of the polyvinyl butyral thenthe adhesion of glass to the polyarylcarbonate is satisfactory and yetthere is no stress cracking or cloudiness developed in the product. Thepolyvinyl acetal is preferably in sheet form and preferably has athickness of from about 2 to about 60 mils most preferably about 5 to 35mils.

Any suitable phosphate may be used. The most suitable phosphates arethose which are highly compatible with the polyvinyl acetal and whichhave little or no adverse eifects on the polyarylcarbonate. Thephosphates with little tendency to attack polyarylcarbonate and whichhave the simultaneous and unique ability to plasticize the polyvinylacetal preferably have the formula:

wherein R is aryl, alkaryl, alkyl or cycloalkyl, with the proviso thatwhen all of the radicals represented by R in a given compound are alkylradicals each must have 5 or more carbon atoms. It is possible for R torepresent different radicals in the same compound. Moreover, mixtures ofthese compounds may be used to plasticize the polyvinyl acetal inaccordance with this invention. The preferred alkyl radicals have 1-9carbon atoms. The most suitable phosphates have the formula Ar lOwherein Ar is aryl or alkaryl such as phenyl, cresyl, tolyl, o-tolyl,mtolyl, m-cumenyl, p-cumenyl, mesityl, 2,3-xylyl and the like. Thepreferred alkaryl radicals are those which have one benzene ring andwhich contain from -1 to 3 carbon atoms per side chain and which havefrom 1 to 3 side chains. Specific examples include triphenyl phosphate,

tri-p-cresyl phosphate, tri-2,3-xy1yl phosprate, trimesityl phosphate,methyl diphenyl phosphate, dimethyl phenyl phosphate, ethyl di-p-cresylphosphate, tripentyl phosphate, trihexyl phosphate, pentyl dihexylphosphate, octyl diphenyl phosphate, triocytyl phosphate, octyldi-p-cresyl phosphate, tricyclohexyl phosphate, cyclohexyl diphenylphosphate, cyclobutyl diphenyl phosphate, trinonyl phosphate and thelike. Tri-p-cresyl phosphate is preferred.

The polyvinyl acetal resins which are employed in the present inventionmay be made from various unsubstituted 'aldehydes or mixtures thereof oreven from unsubstituted ketones containing an active carbonyl group orfrom mixtures of unsubstituted aldehydes and ketones. Thus,formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde,valeraldehyde, hexaldehyde, benzaldehyde, crotonaldehyde, cyclohexanoneand the like and mixtures thereof may be utilized. In general, theacetal resin is made by reacting an aldehyde with hydrolyzed polyvinylester in the presence of a solvent for the product and precipitating theresin product with water. Alternate methods might include carrying outthe reaction in the presence of a non-solvent dispersing medium such aswater or a non-solvent mixture of water and solvent, e.g., awaterethanol mixture. More detailed methods for preparing such resinsare set forth in Morrison et al. US. Patent No. Re.20,4-30, dated June'29, 1937, and 'Lavin et al. US. Patent No. 2,496,480. In general,polyvinyl acetal resins made from saturated lower unsubstitutedaliphatic aldehydes are the most suitable. These would include polyvinylacetal resins made from unsubstituted saturated aliphatic aldehydescontaining less than 6 carbon atoms and especially those made fromformaldehyde, acetaldehyde, butyraldehyde and mixtures thereof.Particularly preferred are polyvinyl acetal resins made frombutyraldehyde. The preferred molecular weight range is 150,000 to250,000.

In general, the polyvinyl acetal resins employed may be considered to bemade up, on a weight basis, of from to hydroxyl groups, calculated aspolyvinyl alcohol, 0 to 40% acetate groups, calculated as polyvinylacetate, and the balance substantially acetal. When the acetal isbutyraldehyde acetal, the polyvinyl acetal resin will preferablycontain, on a weight basis, from 16 to 25% hydroxyl groups, calculatedas polyvinyl alcohol and from 0 to 10% acetate groups, calculated aspolyvinyl acetate, the balance being substantially butyraldehyde acetal.

The laminted article of this invention takes advantage of the unusualmechanical properties of glass, Thus, in accordance with this invention,the function of the polycarbonate is not purely structural. The functionof the polycarbonate is to make the glass function as a structurebearing member even when shattered. Thus, the laminated article of thisinvention retains a large percentage of its load bearing propertieseven. after the glass has been shattered so that a car body can beconstructed where the front and rear windows serve as the solesupporting members for the roof, Such a car body dropper on its top willshatter the glass, but the load bearing prop erties of the laminatedglass are retained sufficiently so that the roof is supported by thismain load bearing column. 'Further illustrations of utility includeairplane windshields, loadbearing walls of buildings, partitions, andthe like.

The polycarbonate, may be any suitable film of polycarbonate such asthat disclosed in US. Patents 3,028,365 and 3,117,019 and is preferablyprepared by reacting di- (rnonohydroxyaryD-alkanes with derivatives ofthe carbonic acid such as phosgene and bischloro-carbonic acid esters ofdi-(monohydroxyaryl)-alkanes.

The aryl residues of the di-(monohydroxyaryl)-alkanes can be alike ordifferent. The aryl residues can also carry substituents which are notcapable of reacting in the conversion into polycarbonates, such ashalogen atoms or alkyl groups, for example, the methyl, ethyl, propyl,or

tert. butyl group. The alkyl residue of the di-(monohydroxyaryl)-alkaneslinking the two benzene rings can be an open chain or a cycloaliphaticring and may be substituted, if desired, for example, by an arylresidue.

Suitable di-(monohydroxyaryl)-alkanes are for example (4,4 dihydroxydiphenyl) methane, 2,2 (4,4- dihydroxy diphenyl) propane, 1,1, (4,4'dihydroxydiphenyl) cyclohexane, 1,1 (4,4 dihydroxy 3,3- dimethyldiphenyl) cyclohexaue, 1,1 (2,2' dihydroxy 4,4 dimethyl diphenyl) butane(boiling point: 185-188 C. under 0.5 mercury gauge), 2,2 (2,2' dihydroxy4,4 di tert. butyl diphenyl)- propane or 1,1 (4,4 dihydroxy diphenyl) 1-phenyl-ethane, furthermore methane derivatives which carry besides twohydroxyaryl groups an alkyl residue with at least two carbon atoms and asecond alkyl residue with one or more carbon atoms, such as2,2-(4,4-dihydroxy diphenyl) butane, 2,2 (4,4 dihydroxydiphenyl) pentane(melting point 149l50 C.), 3,3- (4-,4 dihydroxy diphenyl) pentane, 2,2(4,4 dihydroxy diphenyl) hexane, 3,3 (4,4' dihydroxydiphenyl) hexane,2,2 (4,4' dihydroxy diphenyl)- 4 methyl pentane (melting point l5l152C.), 2,2- (4,4' dihydroxy diphenyl) heptane (boiling point 198-200 C.under 0.3 mm. mercury gauge), 4,4 (4,4- dihydroxy diphenyl) heptane(melting point l58-149 C.), or 2,2 (4,4 dihydroxy diphenyl) tridecanenSuitable di (monohydroxyaryl) alkanes the two aryl residues of which aredifferent are for example 2,2 l-,4- dihydroxy 3 methyl diphenyl) propaneand 2,2- (4,4' dihydroxy 3 methyl 3 isopropyl diphenyl)- butane.Suitable di (monohydroxyaryl) alkanes the aryl residues of which. carryhalogen atoms are for instance 2,2 (3,5,3,5 tetra chloro 4,4dihydroxydiphenyl) propane, 2,2 (3,5,3,5 tetrabromo 4,4- dihydroxydiphenyl) propane, (3,3' dichloro 4,4" dihydroxy diphenyl) methane and2,2 dihydroxy- 5,5 difluoro diphcnyl methane. Suitable di(monohydroxyaryl) alkanes the alkyl residue of which linking the twobenzene rings in substituted by an aryl residue are for instance (4,4'dihydroxy diphenyl) phenyl methane and 1,1 (4,4' dihydroxy diphenyl)phenylethane.

In order to obtain special properties, mixtures of variousdi-(monohydroxyaryl)-alkanes can also be used, thus mixed polycarbonatesare obtained.

The conversion of the aforesaid di-(monohydroxyaryl)-alkanes into highmolecular polycarbonates by reacting with the mentioned derivatives ofthe carbonic acid may be carried out as known in the art. For instancethe di-(monohydroxyaryl)-all-:anes can be re-esterified with carbonicacid diesters, eg. dimethyl-, diethyl-, dipropyl-, dibutyl-, diamyl,dioctyl-, dicyclohexyh, diphenyl and dio,p-tolyl carbonate, at elevatedtemperatures from about to about 320 C. and especially from about toabout 280 C.

The polycarbonates can also be produced by introducing phosgeue intosolutions of di-(monohydroxyaryl)-alkanes in organic bases, such asdimethylaniline, diethylaniline, trimethylamine and pyridine, or intosolutions of di- (monohydroxyaryl)-alkanes in inert organic solvents,such as benzine, ligroine, cyclohexane, methylcyclohexane, benzene,toluene, xylene, chloroform, methylene chloride, carbon tetrachloride,trichloroehylene, dichloroethane, methylacetate and ethylacetate, withthe addition of an acid-binding agent as mentioned above.

A process particularly suitable for producing polycarbonates consists inintroducing phosgene into the aqueous solution or suspension of alkalimetal salts such as lithium, sodium-, potassiumand calcium salts of thedi- (monohydroxyaryl)-alkanes, preferably in the presence of an excessof a base such as lithium-, sodium-, potassiumand calcium hydroxideorcarbonate. The polycarbonate precipitates out from the aqueous solution.

The conversion in the aqueous solution is promoted by the addition ofindilferent solvents of the kind mentioned above which are capable ofdissolving phosgene and eventually the produced polycarbonate.

The phosgene may be used in an equivalent amount. Generally however, itis preferable to use an excess of the phosgene.

Finally it is also possible to react the di-(monohydroxyaryl)-alkaneswith about equimolecular amounts of bischloro carbonic acid esters ofdi-(monohydroxyaryl)- alkanes under corresponding conditions.

In the production of polycarbonates according to the various processesit is advantageous to employ small amounts of reducing agents, forexample sodiumor potassium-sulphide, -sulphite and -dithionite or freephenol and p-tert.-butylphenol.

By adding monotunctional compounds which are capable of reacting withphosgene or with the end groups of the polycarbonates consisting of thechlorocarbonic acid ester group and which terminate the chains, such asthe phenols for instance the phenol, the tert.-butylphenol, thecyclohexylphenol, and 2,2 (4 hydroxyphenol-4'- methoxyphenyl)-propane,further aniline and methylaniline, it is possible to regulate themolecular weight of the polycarbonates in wide limits.

The reaction of the di-(monohydroxyaryl) -alkanes with phosgene or ofthe chlorocarbonic esters of the di-(monohydroxy-aryl)-alkanes may becarried out at room temperature or at lower or elevated temperatures,that is to say at temperatures from the freezing point to the boilingpoint of the mixture. (Column 1, line 31 to column 3, line 1 of3,028,365.) The polycarbonate film preferably has a thickness of fromabout 5 to 250 mils and most preferably from about 60 to about 100 mils.In some cases it may be desirable to use copolymers of various dihydroxyaryl propanes in order to achieve special properties.

Other pellucid materials are disclosed in US. Patent 3,069,301 at column1, lines 62-68 which are rigid and resistant to scratching andessentially non-hydroscopic.

In preparing the final preferred structural glass of this invention, thesheets are assembled one on top of the other with the polycarbonate inthe center sandwiched by polyvinyl butyral sheets and glass sheetsrespectively and then the assembled laminate is subjected to heat andpressure sufficient to cause permanent adherence of one layer to theother. It is preferred to pre-dry the polycarbonate sheets prior toassembling the laminate. After assembly of the laminate, as mentionedabove, it is preferred to warm the assembly. Desirably, the warmassembled laminate is passed through de-airing rolls to lightly adherethe layers together and expel the air. This can subsequently be passedthrough tacking rolls. The Warm lightly adhered laminate is thenpreferably passed into an oil autoclave or other high pressure equipmentand heated to a temperature of about 250 to 350 F. at a pressure ofabout 180 to about 250 psi. for about to minutes. The oil is preferablyallowed to reach temperature before any significant pressure is applied,but it is understood that the pressure is sufiicient to hold thelaminate together during the initial heat-up period in the autoclave.The assembly is allowed to cool to about 150 F. or lower while stillunder pressure and then the pressure is removed and the completeassembly is washed with water and detergent to re-rernove the oil.Laminates prepared in this manner have exceptional load bearingproperties and are suitable for structural or engineering purposes. Itis preferred to use a pressure of about 200 p.s.i. and it is preferredto employ temperatures of about 300 F. in the preparation of thestructural glass laminates.

The structural laminated glass of the invention is useful in many areaswhere it was impossible to use glass heretofore, for example, for thepreparation of Windshields for automobiles which eliminate the need forcornerposts by forming not only the windshield but also the supportingmember for the roof of the automobile.

The invention is further illustrated by the following examples in whichparts are by weight unless otherwise specified. Unless otherwiseindicated, the polyvinyl acetal resin used throughout these examples ispolyvinyl butyral resin having a moisture content of 2.0%, and containsapproximately 21% hydroxyl groups calculated as polyvinyl alcohol andapproximately 2% acetate groups calculated as polyvinyl acetate, thebalance being substantially butyral, average molecular weight is about200,000. About parts of polyvinyl butyral are used with about 40 partsof tri-p-cresyl phosphate. A cake is prepared by mixing together thepolyvinyl butyral and the tricresyl phosphate to prepare a plasticizedcake. The cake is skived to prepare a sheet of the stated thickness.

EXAMPLE 1 A sheet of plate glass about 12 x 12 inches having a thicknessof about mils is covered with a sheet of polyvinyl butyral containingthe tri-p-cresyl phosphate plasticizer about 12 x 12 inches and having athickness of about 15 mils. A sheet of polyarylcarbonate having athickness of about 90 mils which measures about 12 x 12 inches and whichis prepared according to US. Patent 3,117,019 from phosgene and2,2-bis-(4-hydroxy phenyl) propane having a relative viscosity of about1.35 measured in methylene chloride at 25 C. is placed n top of thepolyvinyl butyral. The sheet of polyarylcarbonate is pre-dried in anoven at 250 F for four hours. Then another sheet of polyvinyl butyraland another sheet of glass and another sheet of polyvinyl butyralidentical to the first two sheets are placed on the polycarbonate in theorder named. The assembly is warmed to about 100 F. and the passedthrough de-airing rolls to lightly adhere the layers and expel air. Itis then heated to about 160 F. and passed through tacking rolls. Theassembly is then placed in an oil autoclave and heated to a temperatureof about 275 F. and a pressure of about 200 p.s.i. for about 15 minutes.The temperature is reduced to about F. and then the pressure isreleased. The glass is Washed with detergent and water to remove theoil. A laminate so constructed when impacted with sufiicient force tocrack the glass does not delaminate and therefor retains its loadsupporting capacity.

EXAMPLE 2 The foregoing example is repeated except that the assembly isplaced in the oil autoclave and first heated to about 300 F. over aperiod of about 30 minutes at a pressure barely sufficient to hold thefirst assembly together. A pressure of 200 lbs/in. is then applied forabout 10 minutes. The temperature is reduced to about 150 F. and thepressure is released.

EXAMPLE 3 Example 1 is repeated except that the plate glass is replacedWith chemically tempered glass having a thickness of about 60 mils andsold under the trade name Chemcor by Corning Glass Works.

EXAMPLE 4 Example 1 is repeated except that the polyvinyl butyral isreplaced with polyvinyl formal. This is an acetal resin having amoisture content of about 2.0% and contains approximately 8% hydroxylgroups calculated as polyvinyl alcohol and approximately 11% acetategroups calculated as polyvinyl acetate and the balance substantiallyformaldehyde-acetal. The molecular weight is about 200,000.

EXAMPLE 5.

Example 1 is repeated except that instead of using tricresyl phosphateas the plasticizer for the polyvinyl butyral, triphenyl phosphate isused.

7 EXAMPLE 6 A pre-laminate is prepared by pressing a pre-dried sheet ofthe polyarylcarbonate of Example 1 between two sheets of polyvinylbutyral having the thickness specified in Example 1 by warming thepre-laminate under light adhesion and passing it through rubber pinchrollers. The pre-laminate is then sandwiched between sheets of glass inaccordance with the procedure of Example 1.

It is to be understood that the foregoing examples are for the purposeof illustration and that any other suitable glass, polyvinyl acetal,polyarylcarbonate or the like could be used provided that the teachingsof this disclosure are followed.

Although the invention has been described in considerable detail in theforegoing, it is to be understood that such detail is solely for thepurpose of illustration and that many variations including laminationswhere more than one layer of polyarylcarbonate, more than one layer ofpolyvinyl acetal, more than one layer of glass, etc., other means offorming a stable laminate such as bagging the assembly, evacuating andplacing the bagged assembly in an autoclave, can be made by thoseskilled in the art without departing from the spirit and scope of theinvention except as set forth in the claims.

What is claimed is:

1. A laminated article comprising a sheet of polyarylcarbonate bonded toa sheet of polyvinyl acetal which has been plasticizcd with a phosphatehaving the formula R FOI,

3. A laminated article comprising a sheet of polyarylcarbonate bonded toa transparent panel with a polyvinyl acetal interlayer which has been.plasticized with a phosphate having the formula wherein R is selectedfrom the group consisting of aryl, alkaryl, alkyl and cycloalkyl withthe proviso that when all of the radicals represented by R are alkylradicals, each must have at least 5 carbon atoms.

4. The laminated article of claim 3 wherein said polyvinyl acetal is apolyvinyl butyral which has been plasticized with from about 5 to about60 percent by weight of said phosphate.

5. The laminated article of claim 3 wherein all of the radicals in saidphosphate represented by R are aryl radicals having one benzene ringsystem.

6. The laminated article of claim 3 wherein said article comprises fivelayers composed of a center layer of polyarylcarbonate sandwichedbetween layers of polyvinyl butyral, said sandwich being againsandwiched between layers of glass.

7. A laminated article comprising a polyarylcarbonate bonded to glasswith polyvinyl butyral which has been plasticized with a phosphatehaving the formula AI'3?O4 wherein Ar is aryl.

3. The laminated article of claim 7 wherein said polyvinyl butyral isplasticized with triphenyl phosphate.

9. A laminated article comprising a polyarylcarbonate bonded to glasswith polyvinyl butyral which has been plasticized with tricresylphosphate.

10-. A laminated article comprising a polyarylcarbonate bonded to glasswith polyvinyl butyral which has been plasticized with tricresylphosphate as essentially the sole plasticizer therefor.

11. A laminated article comprising a polyarylcarbonate, bonded to glasswith a polyvinyl butyral interlayer, said polyvinyl butyral beingplasticized with tricresyl phosphate as essentially the sole plasticizertherefor.

12. A laminated article which comprises a sheet of polycarbonatesandwiched between sheets of polyvinyl butyral which has beenplasticized with from about 10 to 45 percent by weight of tricresylphosphate as essentially the sole plasticizer therefor and which is inturn sandwiched between sheets of glass.

1'3. A five layer laminated glass article having high load bearingproperties which comprises a sheet of polyarylcarbonate, two sheets ofpolyvinyl butyral plasticized with tricresyl phosphate in an amount offrom about 10 to 45 percent by weight as essentially the soleplasticizer therefor and two sheets of glass, the fiat surface of eachsheet of polyvinyl butyral being adhesively bonded to said polycarbonatesheet and the other flat surface of said polyvinyl butyral beingadhesively bonded to said glass sheet.

14. A process for the preparation of a laminated article ofpolyarylcarbonate and polyvinyl butyral which comprises pre-drying asheet of polyarylcarbonate and laminating the dry sheet between sheetsof a polyvinyl acetal which has been plasticized with a phosphate havingthe formula wherein R is selected from the group consisting of aryl,alkaryl, alkyl and cycloalkyl with the proviso that when all of theradicals represented by R are alkyl radicals, each must have at least 5carbon atoms.

15. A process for preparing a laminated article which comprisesassembling a sheet of polyarylcarbonate between two sheets of apolyvinyl acctal resin which has been plasticized with a phosphate andsandwiching the resulting assembly between two sheets of glass and subsequently heating the resulting assembly at a temperature of from about250 to about 350 F. at a pressure of about 180 to about 250 lbs/sq. in.for from about 10 to about 15 minutes, said polyarylcarbonate havingbeen pro-dried at a temperature of from about 150 F. to about 250 F. forup to about 4 hours and said phosphate having the formula wherein R isselected from the group consisting of aryl, alkaryl, alkyl andcycloalkyl with the proviso that when all of the radicals represented byR are alkyl radicals, each 'must have at least 5 carbon atoms.

16. A prelaminate comprising at least one sheet of polyarylcarbonatesandwiched between at least two sheets of polyvinyl acetal plasticizedwith a phosphate having the formula wherein R is selected from the groupconsisting of aryl, alkaryl, alkyl and cycloalkyl with the proviso thatwhen all of the radicals represented by R are alkyl radicals, each musthave at least 5 carbon atoms.

References Cited UNITED STATES PATENTS 2,290,193 7/1942 Kirkpatrick161-199 X 2,423,565 7/1947 Rodman 26-0-42 2,425,568 3/1947 Ryan et al.161-199 2,534,102 12/1950 Buckley et al. 161-199 2,787,568 4/1957Koblitz 161-183 OTHER REFERENCES G. E. Lexan: Polycarbonate Resins,Tech. Report CDC-501, January 1962, p. 7.

G. E. Lexan: Polycarbonate Resins, Tech. Report CDC-502, January 1962,pp. 7 and 8.

EARL M. BERGERT, Primary Examiner.

HAROLD ANSHER, Examiner.

